The invention relates to devices for performing anodizing treatment, preferably micro arc anodizing treatment, and it also relates to associated methods.
It is known to treat alloys based on magnesium, aluminum, or titanium by micro arc anodizing. That technique serves to make layers with very low porosity and of hardness that is much greater than the hardness of an amorphous oxide that could be obtained by conventional anodizing such as sulfuric anodic oxidation (SAO), chromic anodic oxidation (CAO), or phosphoric anodic oxidation (PAO). Specifically, in micro arc anodizing treatments, the oxide layer on the surface of the part is formed as a result of generating microelectric discharges leading to the formation of micro arcs that have the ability to raise the temperature of the surface of the part very locally so as to crystallize the amorphous oxide that forms during the anodizing step. In micro arc anodizing treatment, the parts may be immersed in an aqueous electrolyte and they are exposed to oscillating pulses of electrical energy by a specific electronic generator, and if necessary by a counter-electrode of shape matching the parts. Microscopic light-emitting discharges are then visible at the surfaces of such parts, which discharges are due to dielectric breakdowns in the hydroxide layer, and they can be considered as being microplasmas.
The main parameters of the treatment (frequency of the electrical signal, current density, duration for which the parts are immersed in the bath, temperature, . . . ) can be modulated and controlled as a function of the material of the treated part, of its shape, and of the properties desired for the layer of anodizing.
Nevertheless, making a coating by the present micro arc anodizing technique in a large vessel (vessel having a volume of about 0.5 cubic meters (m3)) can present several limits.
Firstly, that technique can involve using a generator delivering high value bipolar currents, given the large surface area of the part(s) for treatment, which can lead to high levels of electricity consumption. Furthermore, it can be difficult to obtain a coating by micro arc anodizing on a part of large area because of the high currents needed for anodizing.
Furthermore, since micro arc anodizing treatment consumes a large amount of energy, the temperature of the electrolyte in prior art bath treatments can be difficult to control. Nevertheless, it is necessary to control the temperature of the bath in order to ensure that the coating is properly made. The desire to regulate the temperature of the bath can lead to using an installation that is relatively complex, thereby significantly increasing the cost of performing the treatment.
Another disadvantage of prior art micro arc anodizing methods is that it can be difficult to measure reliably certain parameters of the electrolyte in the bath while the anodizing treatment is being performed. Reliable measurements of such parameters are nevertheless desirable, e.g. in order to be able to modify the anodizing treatment being performed as a function of the information determined from such measurements.
Finally, in order to perform micro arc anodizing on a part in a well-specified zone, it is possible to use resists that may be of organic type, e.g. a varnish, or of inorganic type, e.g. resulting from conventional anodizing, for the purpose of preventing the micro arc anodizing layer being formed over the entire surface of the part. Resists serve in particular to insulate the surface of the underlying part electrically from the electrolyte, thereby preventing that surface being anodized. Nevertheless, putting resists into place can be relatively expensive and can make the organization of fabrication significantly more complex. Furthermore, the masking step may be difficult to perform and can thus make the treatment significantly more expensive.
There thus exists a need to provide devices that enable anodizing treatment to be performed in simple and inexpensive manner, and in particular micro arc anodizing treatment.
There also exists a need to provide devices that enable the temperature of the electrolyte during anodizing treatment to be controlled effectively, and in particular during micro arc anodizing treatment.
There also exists a need to provide novel devices suitable for performing treatments in addition to anodizing and making it possible in particular to monitor reliably the parameters of the electrolyte in use during the anodizing treatment.